LAS VEGAS -- Welterweight champion Floyd Mayweather Jr. landed so many clean right hands against Robert Guerrero in a one-sided decision win on Saturday night at the MGM Grand Garden Arena that it was no wonder the pound-for-pound king's hand was sore.

Mayweather said after the fight that he hurt his hand late in the bout -- the reason, he said, he was not able to finish Guerrero off and get a knockout.

Mayweather's hand looked swollen and discolored when he showed it to media members after the postfight news conference. The health of Mayweather's hand is critical if he is to return to fight an opponent to be determined on Sept. 14 at the MGM Grand in the second pay-per-view fight of his 30-month, six-fight deal with Showtime/CBS, which Mayweather said will bring him to the end of his fighting career.

Mayweather (44-0, 26 KOs) said at the postfight news conference that he planned to still fight on Sept. 14, and his visit to the doctor after that seemed to match his optimism about keeping the date.